There exists a long-felt need for safe, inexpensive, easy-to-use, and reliable technologies for energy storage. Large scale energy storage enables diversification of energy supply and optimization of the energy grid. Existing renewable-energy systems (e.g., solar- and wind-based systems) enjoy increasing prominence as energy producers explore non-fossil fuel energy sources, however storage is required to ensure a high quality energy supply when sunlight is not available and when wind does not blow.
Electrochemical energy storage systems such as flow batteries have been proposed for large-scale energy storage. But existing flow batteries suffer from a variety of performance and cost limitations, including, for example, optimal separators, decoupling energy and power, system scalability, round trip energy efficiencies (RTEff), cycle life, and other areas.
Despite significant development effort, no flow battery technology has yet achieved widespread commercial adoption, owing to the materials and engineering hurdles that make system economics unfavorable. Accordingly, there is a need in the art for improved flow batteries.
Separators allow mobile ions, such as sodium or potassium, to flow between different electrolyte solutions while restricting the flow of active materials, such as vanadium or iron. Current efficiency of the flow battery is lost due to a variety of factors, including diffusive crossover of active materials, transference crossover of active materials, electrical shorting, parasitic side reactions, and shunt currents. Prior attempts to maximize mobile ion flow while minimizing active material crossover has involved the use of various types of polymers, separator thicknesses and other various techniques. Herein described is a novel solution to the problems associated with separators wherein current and voltage efficiencies are maximized, while separator thickness is minimized for a given current density.